Electric resistance heating element



April 16, 1935. E. 1 wn-:GAND 1,997,844

ELECTRIC RESISTANCE HEATING ELEMENT Filed Jan. 8, 1932 EL. PVegand ,4 from/7 Patented Apr.l 16, 1935 UNITED STATES 1,997,844 ELECTRIC RESISTAE HEATING ELEMENT Edwin L Wiegand, Pittsburgh, Pa.

Application January 8, 1932, Serial No. 585,491

3 Claims.

This invention relates to electric resistance heating apparatus and has for its object the provision of a new, improved, and simplied construction of heating element and a new and im- 5 proved mode of making the same.

In the drawing accompanying and forming a part of this application Figs. 1 and 2 are perspective views of alternative forms of my improved heating element; Figs. 3 to 'I inclusive are en larged detail views illustrating successive steps in the process of manufacturing said elements; Fig. 8 illustrates a. modified form of device; Fig. 9 is a perspective view of one of said elements provided with a plain sheath; Figs. 10 and 1l illustrate my improved elements as provided with ns applied to the naked sheathing; Fig. 12 is a perspective view of one of my units provided with the fins applied to the encased sheathing; and Figs. 13 and v14 are detailviews illustrating two modes of applying the iins to the sheath so as to produce a convenient coverage therefor.

My improved and simplied heating element consists essentially of'a metal sheath closely surrounding a mass of electrically insulating, heatconducting material in which is buried an electric resistance heating wire, the sheath being folded or rolled around the insulating material as a part of the process of making the element, the

result being that one characteristic of my invention is a sheath which is slitted or slotted along one side from end to end. I denotes the sheath, 2 the electrically non-conducting material, and 3 the resistance wire.

In the construction of my improved electric resistance heating unit an elongated strip of sheet-metal, having a width equal to the' circumference of the desired sheath and a length equal to the length of the desired sheath, is rst drawn to the form of an open channel as shown for example in Fig. 3, after which the resistor and the insulating material are introduced and the' channel ,closed laterally to compact the latterV about the former. One method is to cover the bottom of the channelgwith a quantity of the insulating material 2 which is preferably a cementitioussubstance applied in a moist condition. While I do not limit myself to the composition of this material I recommend such substances as alumina., magnesia and zirconia, combined with 'a smaller amount of silica and preferably also con-- taining a very small amount of ball-clay or similar material to constitute a binder. In this material I immerse the electric resistance wire 3, pre-shaped into sinuous or helical form, with its ends twisted about terminals made ci wire oi `Rossum a higher electricalpconductivity, after which a second quantity of similar cementitious material is introduced as shown at 2a in Fig. 6, after which the device is placed between suitable dies '5-5 andthe lips IB of the channel are closed from 5 the dotted line position shown in Fig'. 7 to the form of a closed tube. I have shown the dies as formed with a groove or channel 6 communicating with the seam 'l for the reception of any excess insulating material which may beforced out of 10 the sheath in this operation.

The formed element is now dried and baked at a suicient temperature toY ehydrate the insulating material to a sufficient degree to prevent the occurrence of electrolytic action when oper- 15 ated electrically.

vIn Fig. 1 the terminal wires `1"-4 project at opposite ends; in Figs.,2 and 8 both project from the same end. Any suitable form of terminal block may be employed, a preferred arrangement being that shown in Fig. 13 wherein an insulating bushing 20 is introduced into the end of the sheath and secured by upsetting or rolling the end of the sheath thereover as shown at 2|. Located in this bushing is an externally threaded binding-post 22, having a head 23 inside the bushing, the head and bushing being notchedfor the passage of the wire 4 which is then wrapped about the post beneath the nut 24.

Any suitable or desired cross section can be adopted; in Fig. 1 I have shown a sheath of circular cross-section, in Fig. 2 one of elliptical cross-section, and many others may be used. Also different arrangements of wire and terminals are possible, either for example by locating one terminal 4 at each end of the rod as shown in Fig. 1, or by locating two terminals at the same end as shown at 4a in Fig. 8. It is not necessary to bring the two lips of the sheath into contact with each other, and indeed a slight spacing at this point is advantageous in facilitating the dehydration of the insulating material, although such proximity should be secured as will insure adequate mechanicalstrength.

Due to the construction hereinbefore described a, high degree of uniformity oi location and compression of the insulating material is obtained, also quick and thorough dehydration is secured, but it is desirable to shield the device against the reabsorption of moisture and also in some cases to provide an.- extension of heat dissipating area; this can. bedone in any one of many ways. The simplest mode is to insert the completed 'element into an outer, plain, liquid-tight tube Ill as mown inFig. 9; a second plan is to introduce the element into a tubular shell H provided externally with external flanges l2 as shown in Fig. 10. A third scheme is to surround the element, either with or without an'intervening shell element I3, with iins as shown in Fig. 11, each' n comprising a laterally extending portion I4 and an integral tubular portion of tapered or graduated -diameter so as to fit part ly on the sheath or shell and partly upon the ange of the next succeeding iin. Another plan is to'wind upon the exterior of the element a strip lli as shown in Figs. 12 and 13, one edge of this strip having an outturned fin portion IJ and the opposite margin i8 abutting or underlying the iiange Il] of the adjacent convolution of the strip. l

The essential mode of construction heretofore described enables this resistance-element to be made of long, narrow, shape Without sacrificing the uniformity of distribution and pressure of the insulating-material, and this in turn enables the production of an element having a high degree of heat-dissipating ability, due to the short ,heat-path between theresistance-wire and the sheath and to the close contact between this wire and the heat-conducting material in which it is submerged. The ease of transmission of heat from the resistance-wire to the sheath renders the employment of ns specially impor- -tant in order to secure sufficiently rapid dissipation of this heat, and renders particularly important some mode of applying the fins, such as one of the modes shown in Figs. 11, 12, 13,

4and 14 thereof, wherein firm metal-to-mfetal heat parts issecm'ed Atric heating element in order to indicate that I do not limit myself to any one construction or design or arrangement, and my inventive idea can be embodied in many additional shapes and constructions, as will be understood by those skilled in the art; for which reason I do not limit myself to any details herein shown or described except as the same are4 specifically recited in my several claims which I desire may be constructed each according to its own limitations and independent of limitations contained in other claims. Having thus described my invention what I claim is:

1. The method of producing electrical resistlance heating elements which includes the steps of forming a metal strip into a U-shaped channel the lower part of which is substantially semicylindrical in cross section, lling said semi-cylindrical portion with uent refractory insulating material, partially embedding a heating element in said insulating materiahadding a further quantity of saidinsulating material and then by a single operation bending said strip above said semi-cylindrical portion into serni-cylindrical shape and compressing said insulating material and causing it to conform to and ll the interior ofthe sheath `into which said strip is thus formed.

'2. The method of producing an electrical resistance heating element which inciudes'the steps of bending an elongated metal strip into the form of an open channel, then introducing a mass of uent refractory, insulating material into said channel and embedding a preformed resistor therein, then bending said channel into the form of a tube having a longitudinally ex- Atending slot therein and then applying to the exterior of said tube a metallic shell having a relatively large heat dissipating area and which closes said slot.

3. The method of producing an electrical resistance heating element which includes the steps of bending an elongated metal strip into the form of ari-open channel, then introducing a mass of Aiiuent refractory, insulating material into said channel .and embedding a preformed resistor therein, thenl bending said channel into the form of a tube having a longitudinally extendingslot therein and then winding spirally about said tube a metal strip which is L-shaped in section and which completely encloses said tube and has extended contact therewith,

, EDWIN L. WIEGAND. 

